The literature is replete with various systems and methods for pyrolyzing scrap rubber, such as that found in worn out vehicle tires, into carbon black solids, low density hydrocarbon gases, and liquid hydrocarbon oil. Such a system is described in U.S. Pat. No. 5,894,012, issued to Denison, incorporated by reference, which describes a pyrolysis subsystem, a carbon black refinement subsystem, and a pyrolysis oil subsystem. Such systems accept feedstock consisting of shredded vehicle tires, pyrolyze the shreds to produce hydrocarbons and an impure carbon black. The system may comprise additional subsystems to further refine the hydrocarbons and/or carbon black. These additional subsystems will remove any metals and fiberglass shards from the carbon black byproduct for produce a fairly high grade carbon black containing metal oxide particles and sulfur particles remaining from the devulcanizaton action provided by the basic pyrolysis process.
It has been found through experience that while the carbon black produced by such systems can be of exceedingly high grade, it still contains chemical impurities which are difficult to remove. For example, carbon black reclaimed from scrap tires contains about 2.5 wt % sulfur as well as metallic impurities and silica, and these impurities are inherent in the carbon black resulting from the pyrolysis of tire shreds. Such impurities render this carbon black unsuitable for products which require a very highly refined grade of carbon black, such as toners for use in xerography equipment and laser printers. Such highly refined carbon black is normally produced directly from hydrocarbons which have few impurities to begin with, and not from scrap rubber which contains high amounts of sulfur and zinc compounds. If an economical way could be found to further refine the carbon black resulting from various scrap rubber pyrolysis processes of the prior art, then the value of the pyrolysis process could be enhanced by the higher marketability of the resulting carbon black byproduct. Such a product might also be highly competitive with existing processes producing toner black directly from hydrocarbons.
Accordingly, what is needed is an improved system, process, and apparatus for refining and purifying carbon black produced as a byproduct of scrap rubber pyrolysis processes, and in particular, from scrap rubber provided by shredded vehicle tires.